Thermal decomposition of protein in soil organic matter

Infrared spectroscopy and nitrogen analyses suggest that secondary amide groups in protein-like components of soil clay-organic complexes and extracted organic matter decompose above 100°C to yield ammonia which is retained as NH₄⁺ by acid-washed clay-organic complexes. Above about 400°C, other volatile nitrogenous decomposition products are released. Clay surfaces in the clay-organic complexes may catalyse the decomposition.     

THE EFFECT OF PESTICIDES ON THE YIELD AND BOTANICAL COMPOSITION OF A NEWLY-SOWN RYEGRASS LEY AND OF AN OLD MIXED PASTURE

Newly-sown S24 perennial ryegrass at Hurley and old established ryegrass-dominant mixed pasture at Rothamsted were treated with several pesticides, singly and in combination, over the period 1969–73. Yields were either unaffected or increased by up to 30% in any one year, depending on the treatment, the newly-sown sward giving the more consistent response from year to year.     

THE EFFECT OF CUTTING HEIGHT AND NITROGEN LEVEL ON THE YIELD, IN VITRO DIGESTIBILITY AND CHEMICAL COMPOSITION OF ITALIAN RYEGRASS SWARDS

Three cutting heights, 2±5, 7±6 and 12±7 cm (1, 2±5 and 5 in.) and three levels of fertilizer N, 168, 280 and 392 kg N/ha (150, 250 and 350 Ib N/ac) were imposed on a sward of Italian ryegrass (Lolium multiflorum) cv. Irish. Lowering the cutting height and increasing the level of applied N increased the yield of herhage DM. Increasing the level of applied N had a greater effect on the chemical composition of the herbage than altering the cutting height     

Laboratory incubation studies of chlorophenoxyacetic acids in chernozemic soils

The relative persistence of 2,4-D, MCPA and 2,4,5-T in some Saskatchewan soils was assessed under laboratory conditions. Under moist conditions, 2,4-D and MCPA showed half-life times of between 14 and 41 days but the MCPA half-life was usually 1 or 2 days longer. 2,4,5-T exhibited a half-life period over twice the length of the other chemicals. The half-life times were directly correlated to microbial plate counts, the larger numbers of soil microorganisms being associated with shorter residence times. Half-lives depended on soil moisture content and the best moisture levels for chemical loss appeared to be just less than field capacity. The use of ¹⁴C in 2,4-D incubation studies showed that the initial cleavage of the 2,4-D molecule was associated with the ether linkage and was not a decarboxylation.     

The redox characteristics of four peat profiles

In several previous observations on peat soils, redox potentials appeared to vary with season and depth. To clarify this variation, a systematic study was made over 1 yr at four peat sites, including wet and dry areas at high and low altitude in northern England.The coefficients of linear regressions of redox potential on seasonal temperatures became progressively more negative with increasing depth at all four sites. These observations support an hypothesis that increased aeration accompanying increased temperature played a role at the surface, but was of less importance in the deeper layers, where the reducing conditions that result from microbial activity were dominant.By using orthogonal polynomials, it was possible to demonstrate the existence of redox minima in the profiles at all sites. There were rather more minima present using this method at the lowland sites that at the upland ones where trends of redox with depth were otherwise linear or non-significant. Although the mean redox potentials over whole profiles were lower in the wetter sites than the drier, the mean depths of the redox minima were similar. These mean depths were poorly defined however having standard deviations of 30–50 per cent of the means calculated from the year's observations.Finally, it was shown that although the potentials were measured 60 s after closing the circuit, very similar conclusions would have been reached if the readings had been taken after 10 s.     

The arthropods associated with the decomposition of some common grass and weed species in the soil

The arthropod fauna associated with the decomposition of herbage of various species on the surface of the soil was studied. Litter of Rumex, Urtica, Ranunculus, Senecio and Lolium disappeared rapidly at first and thereafter at a slower rate. Dactylis disappeared more slowly than the other litters over the first 6$\text{1}\text{2}$ months but its rate of disappearance thereafter was greater than that of the other species. There were quantitative and qualitative differences between the microarthropod communities associated with the various litters. Highest populations of microarthropods were recorded from Dactylis. Dactylis and Lolium were the most similar in the species composition of their faunas. Changes occurred in the relative abundance of various arthropod groups and species during the course of decomposition in all litters.     

The abundance of Trichoderma propagules and the distribution of species in forest soils

Propagules of Trichoderma generally formed less than 3 per cent of the total fungal propagules in a variety of forest soils in the southeastern U.S. and Washington State. The largest populations were found in the F and H organic horizons of the forest floor or under conditions of excessive moisture. T. viride Pers. ex S.F. Gray and T. polysporum (Link ex Pers.) Rifai were largely restricted to cool temperate regions; whereas, T. harzianum Rifai was characteristic of warm climates. T. koningii Oud. and T. hamatum (Bon.) Bain, were the most widely distributed species aggregates and were found in all the climatic regions investigated. Under conditions of excessive moisture, strains of T. hamatum and T. pseudokoningii Rifai were the dominant forms.     

Isolation and characterization of Thiobacillus from alkali soils

Alkali soils are poor in sulphur-oxidizing bacteria. By appropriate enrichment, two bacterial strains resembling Thiobacillus thiooxidans and T. novellus have been isolated from an alkali soil. The strain of T. novellus possesses characteristics which make it suitable in reclamation of alkali soils by sulphur amendment.